Method and apparatus for improving fan case containment and heat resistance in a gas turbine jet engine

ABSTRACT

A method and apparatus for improving fan case containment in a gas turbine jet engine employs a containment ring and a heat resistance ring which are shrink interference fit on the inside diameter of the fan case, the containment ring where the large fan blades turn, and the heat resistance ring where heated air from backfiring heats up the fan case. The containment ring is made of a super alloy to provide added strength to the fan case should a fan blade break, containing the fan blade within the fan case. The heat resistance ring is made of titanium or other suitable material. Additionally, one or more stiffener rings are shrink interference fit on the outside diameter of the fan case. The containment ring and stiffener rings can reduce the flight weight of the fan case and lower the material costs, while increasing the containment strength of the fan case.

FIELD OF THE INVENTION

This invention relates to gas turbine jet engines, and more particularlyto fan case containment of gas turbine jet engines, and even moreparticularly to a method and apparatus for improving fan casecontainment and heat resistance.

BACKGROUND OF THE INVENTION

In a full test of a gas turbine jet engine, a fan blade is deliberatelyreleased from the hub at a maximum engine rotation speed by an explosivebolt positioned at the base of the fan blade. This test is used todemonstrate the engine carcass's ability to contain the impact of thefan blade and handle the resulting out-of-balance forces. This impact isabsorbed as vibration through the fan case containment system whichsurrounds the engine. The fan case is the key element in fan casecontainment and is typically the heaviest component of a gas turbine jetengine due to its size, and due to the strength requirements the fancase must possess for containment purposes. In gas turbine jet enginessusceptible to backfiring, heated air travels backward from thecombustor to the fan area, increasing the temperature within the fancase and causing a rise in fan case temperature. These highertemperatures may be a factor in determining what material the fan casemust be constructed. Maintaining or reducing the weight of the fan case,while at the same time maintaining or improving fan case containmentstrength and utilizing fan case materials that can withstand the fancase temperatures is a demonstrated need in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the overall structure of a typicalgas turbine jet engine with a fan casing typical of the prior art.

FIG. 2 shows a cross section of a forging for a fan casing typical ofthe prior art.

FIG. 3 shows a cross section of a forging for a fan casing for improvedfan case containment in an embodiment of the present invention.

FIG. 4 shows a cross section of a machine finished fan casing having twostiffener rings (FIGS. 5A, 5B and 6A, 6B) and a containment ring (FIGS.7A, 7B) that have been shrink interference fit to the fan casing of FIG.3 in an embodiment of the present invention.

FIG. 5A shows a cross section of a forging for a first stiffener ringfor the fan casing of FIG. 3 in an embodiment of the present invention.

FIG. 5B shows the first stiffener ring of FIG. 5A about to be shrinkinterference fit to the fan casing of FIG. 3 in an embodiment of thepresent invention.

FIG. 6A shows a cross section of a forging for a second stiffener ringfor the fan casing of FIG. 3 in an embodiment of the present invention.

FIG. 6B shows the second stiffener ring of FIG. 6A about to be shrinkinterference fit to the fan casing of FIG. 3 in an embodiment of thepresent invention.

FIG. 7A shows a cross section of a forging for a containment ring forthe fan casing of FIG. 3 in an embodiment of the present invention.

FIG. 7B shows the containment ring of FIG. 7A about to be shrinkinterference fit to the fan casing of FIG. 3 in an embodiment of thepresent invention.

FIG. 8 shows a schematic diagram of the airflow through a typical gasturbine jet engine.

FIG. 9 shows a schematic diagram of the airflow through a typical gasturbine jet engine susceptible to backfiring.

FIG. 10 shows a cross section of a forging for a fan casing for improvedheat resistance in an embodiment of the present invention.

FIG. 11 shows a cross section of a machine finished fan casing having aring of heat resistant material that has been shrink interference fit tothe fan casing of FIG. 10 in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the Figures, in which like reference numerals and namesrefer to structurally and/or functionally similar elements thereof, FIG.1 shows a schematic diagram of the overall structure of a typical gasturbine jet engine with a fan casing typical of the prior art. Referringnow to FIG. 1, Gas Turbine Jet Engine 100 has Fan 102 having a pluralityof Fan Blades 104 for air intake and thrust housed within Fan Case 106.Booster 108 is a low pressure compressor which feeds inlet air to HighPressure Compressor Rotor 110 and its attached blades and stators, whichforce air into Combustor 112, increasing the pressure and temperature ofthe inlet air. High Pressure Turbine Rotor 114 and its accompanyingblades and stators are housed within High Pressure Turbine Case 116. LowPressure Turbine Rotor 118 and its accompanying blades and stators arehoused within Low Pressure Turbine Case 120. Low Pressure Turbine Rotor118 and its accompanying blades and stators extracts energy from thehigh-pressure, high-velocity gas flowing from Combustor 112 andtransfers energy to Low Pressure Turbine Shaft 122, which in turn drivesFan 102, providing most of the thrust for Gas Turbine Jet Engine 100.

FIG. 2 shows a cross section of a forging for a fan casing typical ofthe prior art. Referring now to FIG. 2, Fan Case Forging 200 aftermachining yields Fan Case 202, shown in dotted line outline. In thisexample, Fan Case Forging 200 is forged from a titanium cylinder in onepiece. The operating temperatures and load characteristics of theparticular gas turbine jet engine that Fan Case 202 is designed forrequires that Fan Case 202 be made of titanium. The forging weight forthis particular Fan Case Forging 200 is approximately 3,347 pounds.After machining, Fan Case 202 has a flight weight of approximately 975.2pounds. On gas turbine jet engines, the fan case may also be made ofaluminum, steel, or manufactured from composite materials. Compositematerials consist of a core material, a reinforcing material, and aresin binder. Core materials are typically wood, foam, and honeycomb.Reinforcing materials include fiberglass, carbon fiber, and Kevlar®. Theresin component consists typically of polyesters, vinyl esters, andepoxies. As technology improves, and temperatures go up in the gasturbine jet engines, aluminum cases are often wrapped with Kevlar® togive added strength for fan case containment purposes. For even higheroperating temperatures not appropriate for aluminum or steel, titaniumis used, which may also by wrapped with Kevlar® if so needed foradditional strength.

Structural features of the machined Fan Case 202 include FirstStiffening Ring 204 and Second Stiffening Ring 206. These two stiffeningrings help prevent Fan Case 202 from going oval under the load andtemperature conditions experienced during engine operation. AccessoryFlange 208 will have holes drilled through it and various enginecomponents hung from it, such as gear boxes, tubes, wiring, etc. FirstContainment Ring 210 encircles the outside of Fan Case 202 and providesadditional strength for fan case containment. Second Containment Ring212 circles the inside of Fan Case 202 and also provides additionalstrength for fan case containment. The section of Fan Case 202 betweenFirst Containment Ring 210 and Second Containment Ring 212 is the regionwhere a fan blade, such as Fan Blade 104 (FIG. 1) will strike should itbreak loose from its hub. Due to the size of the Fan Blades 104, whichtypically are the largest fan blades in a gas turbine jet engine, thissection of Fan Case 202 must be exceptionally strong. Thus, First andSecond Containment Rings 210, 212 provide the additional strengthrequired.

FIG. 3 shows a cross section of a forging for a fan casing in anembodiment of the present invention. Referring now to FIG. 3, a fancasing of the present invention can be substituted for Fan Case 202 foruse in the same gas turbine jet engine for which Fan Case 202 wasdesigned. Fan Case Forging 300 after machining yields Fan Case 302,shown in dotted line outline. In this example, Fan Case Forging 300 isalso forged from a titanium cylinder in one piece, but is of a simplershape which simplifies the forging process. The forging weight for FanCase Forging 300 is approximately 2,595 pounds, 752 pounds lighter thanFan Case Forging 200. After machining, Fan Case 302 has a flight weightof approximately 751.3 pounds, 223.9 pounds lighter than Fan Case 202.

Structural features of the machined Fan Case 302 include FirstStiffening Ring Notch 304 and Second Stiffening Ring Notch 306 locatedin a middle portion of Fan Case 302. Two stiffening rings from twoadditional forgings (see FIGS. 5A, 5B, 6A, and 6B) will be seated inFirst Stiffening Ring Notch 304 and Second Stiffening Ring Notch 306(see FIG. 4) to help prevent Fan Case 302 from going oval under the loadand temperature conditions experienced during engine operation.Depending upon the design of a particular fan case, more or lessstiffening ring notches may be required, and they may be located invarious positions on the outer surface of the fan case. Accessory Flange308 towards the back end of Fan Case 302 will have holes drilled throughit and various engine components hung from it, such as gear boxes,tubes, wiring, etc.

Containment Ring Notch 310 circles the inside of Fan Case 302circumferentially at the front end. A containment ring from anadditional forging (see FIGS. 7A and 7B) will be seated in ContainmentRing Notch 310. The section of Fan Case 302 spanning Containment RingNotch 310 is the region where a fan blade, such as Fan Blade 104(FIG. 1) will strike should it break loose from its hub. This section ofFan Case 302 must be exceptionally strong, and the containment ring fromthe additional forging, machined to a predetermined shape to match withContainment Ring Notch 310, provides the additional strength. Fan Case302 has no structure comparable to First Containment Ring 210 which isno longer needed with Fan Case 302 of the present invention due to theadditional strength provided by the containment ring.

FIG. 5A shows a cross section of a forging for a first stiffener ringfor the fan casing of FIG. 3 in an embodiment of the present invention,and FIG. 5B shows the first stiffener ring of FIG. 5A about to be shrinkinterference fit to the fan casing of FIG. 3 in an embodiment of thepresent invention. Referring now to FIGS. 5A and 5B, First StiffeningRing Forging 500, after machining to a predetermined shape to match withFirst Stiffening Ring Notch 304, yields First Stiffening Ring 502, shownin dotted line outline in FIG. 5A. In this example, First StiffeningRing Forging 500 is forged from an aluminum ring in one piece. Theforging weight for First Stiffening Ring Forging 500 is approximately154 pounds. After machining, First Stiffening Ring 502 has a flightweight of approximately 41 pounds.

First Stiffening Ring 502 is shrink interference fit into FirstStiffening Ring Notch 304. At ambient temperature, the inside diameterof First Stiffening Ring 502 will be slightly smaller than the outsidediameter of First Stiffening Ring Notch 304. First Stiffening Ring 502is heated, which causes First Stiffening Ring 502 to expand, increasingthe inside diameter to a diameter that is greater than the outsidediameter of First Stiffening Ring Notch 304, and giving rise to FirstRing Clearance 504, enabling First Stiffening Ring 502 to be positionedas shown in First Stiffening Ring Notch 304. In this position, FirstStiffening Ring 502 is allowed to cool, which shrinks in diameter andseats itself circumferentially into First Stiffening Ring Notch 304. Atambient temperature, due to First Stiffening Ring 502 wanting to returnto its smaller inside diameter, but being prevented from doing so due tothe larger outside diameter of First Stiffening Ring Notch 304, a shrinkwith an interference fit results, with compressive circumferential forcebeing applied to Fan Case 302 by First Stiffening Ring 502, and tensilecircumferential force is applied to First Stiffening Ring 502 by FanCase 302.

FIG. 6A shows a cross section of a forging for a second stiffener ringfor the fan casing of FIG. 3 in an embodiment of the present invention,and FIG. 6B shows the second stiffener ring of FIG. 6A about to beshrink interference fit to the fan casing of FIG. 3 in an embodiment ofthe present invention. Referring now to FIGS. 6A and 6B, SecondStiffening Ring Forging 600, after machining to a predetermined shape tomatch with Second Stiffening Ring Notch 306, yields Second StiffeningRing 602, shown in dotted line outline in FIG. 6A. In this example,Second Stiffening Ring Forging 600 is forged from an aluminum ring inone piece. The forging weight for Second Stiffening Ring Forging 600 isapproximately 148 pounds. After machining, Second Stiffening Ring 602has a flight weight of approximately 40.6 pounds.

Second Stiffening Ring 602 is shrink interference fit into SecondStiffening Ring Notch 306. At ambient temperature, the inside diameterof Second Stiffening Ring 602 will be slightly less than the outsidediameter of Second Stiffening Ring Notch 306. Second Stiffening Ring 602is heated, which causes Second Stiffening Ring 602 to expand, increasingthe inside diameter to a diameter that is greater than the outsidediameter of Second Stiffening Ring Notch 306, and giving rise to SecondRing Clearance 604, enabling Second Stiffening Ring 602 to be positionedas shown in Second Stiffening Ring Notch 306. In this position, SecondStiffening Ring 602 is allowed to cool, which shrinks in diameter andseats itself circumferentially into Second Stiffening Ring Notch 306. Atambient temperature, due to Second Stiffening Ring 602 wanting to returnto its smaller inside diameter, but being prevented from doing so due tothe larger outside diameter of Second Stiffening Ring Notch 306, ashrink with an interference fit results, with compressivecircumferential force being applied to Fan Case 302 by Second StiffeningRing 602, and tensile circumferential force is applied to SecondStiffening Ring 602 by Fan Case 302.

FIG. 7A shows a cross section of a forging for a containment ring forthe fan casing of FIG. 3 in an embodiment of the present invention, andFIG. 7B shows the containment ring of FIG. 7A about to be shrinkinterference fit to the fan casing of FIG. 3 in an embodiment of thepresent invention. Referring now to FIGS. 7A and 7B, Containment RingForging 700, after machining to a predetermined shape to match withContainment Ring Notch 310, yields Containment Ring 702, shown in dottedline outline in FIG. 7A. In this example, Containment Ring Forging 700is forged from a ring of nickel-base super alloy, such as Inconel 718,in one piece. The forging weight for Containment Ring Forging 700 isapproximately 467 pounds. After machining to the predetermined shape,Containment Ring 702 has a flight weight of approximately 138.1 pounds.

Containment Ring 702 is shrink interference fit into Containment RingNotch 310. At ambient air temperature the outside diameter ofContainment Ring 702 will be slightly larger than the inside diameter ofContainment Ring Notch 310. Fan Case 302 is heated, which causes FanCase 302 to expand, increasing the inside diameter to a diameter that isgreater than the outside diameter of Containment Ring 702, and givingrise to Containment Ring Clearance 704, enabling Containment Ring 702 tobe positioned as shown in Containment Ring Notch 310. In this position,Fan Case 302 is allowed to cool, which shrinks in diameter and allowsContainment Ring 702 to seat itself circumferentially into ContainmentRing Notch 310. At ambient temperature, due to Fan Case 302 wanting toreturn to its smaller inside diameter, but being prevented from doing sodue to the larger outside diameter of Containment Ring 702, a shrinkwith an interference fit results, with compressive circumferential forcebeing applied to Containment Ring 702 by Fan Case 302, and tensilecircumferential force is applied to Fan Case 302 by Containment Ring702.

For a fan case manufactured from composite material, Containment Ring702 is cooled with liquid nitrogen to reduce its outside diameter givingrise to Containment Ring Clearance 704, enabling Containment Ring 702 tobe positioned as shown in Containment Ring Notch 310. In this position,Containment Ring 702 is allowed to warm up to ambient temperature,increasing in diameter, and seating itself circumferentially intoContainment Ring Notch 310. At ambient temperature, due to ContainmentRing 702 wanting to return to its greater outside diameter, but beingprevented from doing so due to the smaller inside diameter ofContainment Ring Notch 310, an interference fit results, withcompressive circumferential force being applied to Containment Ring 702by Fan Case 302, and tensile circumferential force is applied to FanCase 302 by Containment Ring 702. One skilled in the art will recognizethat a combination of heating Fan Case 302 along with coolingContainment Ring 702 may also be employed in certain situations toeffect a shrink fit.

In one embodiment of the invention, Containment Ring Notch 310 ismachined circumferentially with a reverse taper such that the insidediameter of Fan Case 302 at point A is less than the inside diameter ofFan Case 302 at point B. The taper may vary from fan case to fan case,ranging from just greater than 0° for a cylindrical case to anappropriate degree that would depend upon the specific geometry of aconical fan case. Containment Ring 702 is machined circumferentially onits outside surface to match this same reverse taper. Even thoughContainment Ring 702 is shrink interference fit onto Fan Case 302, thetaper adds extra security so that Containment Ring 702 will not slipaxially on Fan Case 302, which could possibly happen if Containment RingNotch 310 was manufactured without the taper.

In addition, the machining for Fan Case 302 may be done in a firstdirection, such as radially, and the machining for Containment Ring 702may be done in a second direction, such as axially, which is more orless perpendicular to the first direction. Since machining leaves aspiral, or record, continuous groove on the machined surfaces, thegrooves on each surface will align in a cross-hatch manner to eachother, increasing the frictional forces between the two surfaces andreducing the potential for spinning of Containment Ring 702 withinContainment Ring Notch 310. The plurality of grooves on Containment Ring702, which is made of a nickel-base super alloy, are harder than theplurality of grooves on Containment Ring Notch 310 of Fan Case 302,which is made of titanium, or in other fan casings, possibly steel oraluminum. The nickel-base super alloy grooves will dent into the softertitanium, steel, or aluminum grooves. Alternatively, Containment Ring702 could simply be spot welded in one or more locations to ContainmentRing Notch 310, or bolted to one or more flanges secured to ContainmentRing Notch 310, to keep Containment Ring 702 from spinning in relationto Containment Ring Notch 310. Machining in cross directions would notbe needed in this case.

FIG. 4 shows a cross section of a machine finished fan casing having twostiffener rings (FIGS. 5A, 5B, 6A, and 6B) and a containment ring (FIGS.7A and 7B) that have been shrink interference fit to the fan casing ofFIG. 3 in an embodiment of the present invention. Referring now to FIG.4, Containment Ring 702 replicates part of the structure comparable toSecond Containment Ring 212, and eliminates the need for FirstContainment Ring 210 entirely. By shrink interference fittingContainment Ring 702 on the inside diameter of Fan Case 302, as opposedto the outside, the harder super alloy of Containment Ring 702 providesthe initial striking surface should a blade break off. The softertitanium, steel, or aluminum, of Fan Case 302 on the outside ofContainment Ring 702 acts as a shock absorber due to the differentexpansion rates between the two materials. As the super alloy ofContainment Ring 702 begins to move, it pushes against the titanium,steel, or aluminum of Fan Case 302 with a different coefficient ofexpansion. This is like having two nets close to each other. The superalloy of Containment Ring 702 takes the initial blow, and some of theforce is transferred to the titanium, steel, or aluminum Fan Case 302like a shock absorber.

First Stiffening Ring 502 and Second Stiffening Ring 602 are shownseated in First Stiffening Ring Notch 304 and Second Stiffening RingNotch 306 respectfully. First Stiffening Ring 502 and Second StiffeningRing 602 provide stiffening to prevent Fan Case 302 from deformingout-of-round, or going oval, during operation of the engine undertemperature and load conditions.

In this particular example, Table 1 below shows a comparison of theforge and flight weights, and costs, of prior art Fan Case 202 comparedto Fan Case 302 of the present invention. TABLE 1 Forge Wt. Flight Wt.Cost/ Part/Material (lbs) (lbs) lb Total Cost Fan Case 202 Titanium3,347.0 975.2 $8.00 $26,776.00 Fan Case 302 Titanium 2,595.0 751.3 $8.00$20,760.00 First Stiffening Ring 502 154.0 40.5 $1.50 $231.00 AluminumSecond Stiffening Ring 602 148.0 40.6 $1.50 $222.00 Aluminum ContainmentRing 702 467.0 138.1 $7.00 $3,269.00 Inconel 718 Total 3,364.0 970.5$7.28 $24,482.00 Savings −17.0 4.7 $0.72 $2,294.00

Thus, in this example, though the forge weight is 17 pounds more, theflight weight is 4.7 pounds less. In addition, the average cost perpound of the materials for Fan Case 302 is $0.72 per pound less thanthat of Fan Case 202, resulting in a total savings of $2,294.00. Thebiggest advantage, however, is the increased fan case containmentstrength of Fan Case 302 over Fan Case 202. In this example, Fan Case302 is considerably stronger than Fan Case 202.

In other applications, the savings could be more significant. Forexample, for a fan casing that requires Kevlar® reinforcement, a fancasing of the present invention may be sufficiently stronger so as toeliminate the need for the Kevlar® reinforcement, which would be asubstantial savings in both materials cost and labor. The presentinvention could also be used with Kevlar® reinforcement to attain higherfan case containment strength. For gas turbine jet engines thatcurrently use steel or titanium for the fan casings, the presentinvention may enable aluminum to be substituted for the steel ortitanium, and the strength needed for containment provided for by thenickel-base super alloy containment ring. Since the same volume ofaluminum or titanium is about 30%-55% of the weight of the same volumeof steel, substantial weight savings will result. This weight savings isdirectly translated into increased cargo carrying capability or reducedfuel costs or a combination of both.

In the gas turbine jet engine industry, the trend is toward making fanblades longer to increase thrust. The tips of the fan blades can rotateat supersonic speeds, while the base of the fan blades rotate atsubsonic speeds. This can cause a harmonic vibration in the bladesresulting in the tips of the blades breaking off. To counter thisproblem, instead of making straight fan blades, the blades are shapedmore like wide paddles. These wider and longer blades result in moremass that must be contained within the fan casing. Also, as enginesbecome more efficient, they operate at hotter temperatures, adding moredifficulty to the containment problem. The present invention can greatlyassist in meeting these challenges for greater fan case containmentstrength and potentially less overall weight and lower cost.

FIG. 8 shows a schematic diagram of the airflow through a typical gasturbine jet engine. Referring now to FIG. 8, for a gas turbine jetengine not susceptible to backfiring, Air Flow 824 flows into Fan Case806 and into Booster 808. High Pressure Compressor Rotor 810 compressAir Flow 824 as it enters Combustor 812. After passing through the highpressure and low pressure turbines, Air Flow 824 flows out of the backof Gas Turbine Jet Engine 800. The heated Air Flow 824 in Combustor 812only travels on through and out of the back of Gas Turbine Jet Engine800.

FIG. 9 shows a schematic diagram of the airflow through a typical gasturbine jet engine susceptible to backfiring. Referring now to FIG. 9,in contrast to FIG. 8, Gas Turbine Jet Engine 900 is susceptible tobackfiring, which causes a portion of Air Flow 924, Heated Air 926represented by dotted lines, to flow backwards through Gas Turbine JetEngine 900 and into the area of Fan 902. Heated Air 926 causes thetemperature within Fan Case 906 to rise, which also elevates thetemperature of Fan Case 906 itself in the area designated generally byArea 928. Temperature is of course one of the primary factors indetermining what material Fan Case 906 must be constructed. When fancase temperatures rise above 800 degrees, aluminum may no longer besuitable. More expensive heat tolerant materials, such as steel,titanium, or super alloys, may be required.

FIG. 10 shows a cross section of a forging for a fan casing for improvedheat resistance in an embodiment of the present invention. Referring nowto FIG. 10, for gas turbine jet engines susceptible to backfiring, a fancasing of the present invention can be used to counteract the heatproblems and improve the heat resistance of Fan Case 1002. Fan CaseForging 1000 is similar to Fan Case Forging 300 shown in FIG. 3. FanCase Forging 1000 after machining yields Fan Case 1002, shown in dottedline outline, which is similar to Fan Case 302. In this example, FanCase Forging 1000 is forged from aluminum in one piece.

Structural features of the machined Fan Case 1002 are similar to thatshown in FIGS. 3 and 4 but also includes Heat Resistance Ring Notch 1012which circles the inside of Fan Case 1002 circumferentially at thelocation defined generally by Area 928 in FIG. 9. A ring of heatresistant material will, with a shrink interference fit, be seated inHeat Resistance Ring Notch 1012. The section of Fan Case 1002 spanningHeat Resistance Ring Notch 1012 is the region where the heated air frombackfiring causes increased fan case temperatures.

As described above, the machining for Fan Case 1002 may be done in afirst direction, such as radially, and the machining for Heat ResistanceRing 1112 may be done in a second direction, such as axially, which ismore or less perpendicular to the first direction. Since machiningleaves a spiral, or record, continuous groove on the machined surfaces,the grooves on each surface will align in a cross-hatch manner to eachother, increasing the frictional forces between the two surfaces andreducing the potential for spinning of Heat Resistance Ring 1112 withinHeat Resistance Ring Notch 1012. The plurality of grooves on HeatResistance Ring 1112, which is made of titanium, are harder than theplurality of grooves on Heat Resistance Ring Notch 1012 of Fan Case1002, which is made of aluminum. The titanium grooves will dent into thesofter aluminum grooves. Alternatively, Heat Resistance Ring 1112 couldsimply be spot welded in one or more locations to Heat Resistance RingNotch 1012, or bolted to one or more flanges secured to Heat ResistanceRing Notch 1012, to keep Heat Resistance Ring 1112 from spinning inrelation to Heat Resistance Ring Notch 1012. Machining in crossdirections would not be needed in this case.

FIG. 11 shows a cross section of a machine finished fan casing having aring of heat resistant material that has been shrink interference fit tothe fan casing of FIG. 10 in an embodiment of the present invention.Referring now to FIG. 11, Heat Resistance Ring 1112 is shown shrinkinterference fit on the inside diameter of Fan Case 1002 in HeatResistance Ring Notch 1012. In this example, Heat Resistance Ring 1112is made of titanium, but may also be made of other materials that have acombination of heat resistant properties and strength properties tomaintain the structural integrity required for Fan Case 1002 such assteel, steel alloy, or any number of commonly used aerospace superalloys. Heat Resistance Ring 1112 may be fabricated from titanium sheetmaterial that is cut, bent into a cylindrical shape, welded along theseam, and formed to match the inside diameter of Heat Resistance RingNotch 1012. Heat Resistance Ring 1112 may also be forged as describedabove.

The shrink with interference fit may be accomplished, as describedabove, by heating Fan Case 1002, causing it to expand in diameter andallowing Heat Resistance Ring 1112 to be slid into place, where uponcooling, Fan Case 1002 and Heat Resistance Ring 1112 apply force to eachother in a shrink interference fit. Alternatively, Heat Resistance Ring1112 may be cooled with liquid nitrogen, reducing its outside diameterand enabling Heat Resistance Ring 1112 to be slid into Heat ResistanceRing Notch 1012. Also, a combination of heating Fan Case 1002 andcooling Heat Resistance Ring 1112 may be employed to secure the shrinkinterference fit. The titanium of Heat Resistance Ring 1112 is notweakened structurally by the fan case temperatures, and serves as abuffer to the aluminum Fan Case 1002 due to the different expansionrates between the two materials. The titanium of Heat Resistance Ring1112 is exposed to internal fan case temperatures, and some of the heatis transferred to the aluminum Fan Case 1102. The titanium provides thestrength needed that the aluminum lacks at the higher temperatures.Containment Ring 1102 may be made from a super alloy.

First Stiffening Ring Notch 1104 and Second Stiffening Ring Notch 1106may be made of aluminum, titanium, or steel. Depending upon the specificgas turbine jet engine being considered, a containment ring and one ormore stiffening rings may not be necessary with a heat resistance ring,and a heat resistance ring may not be necessary with a containment ringand one or more stiffening rings. The present invention gives the enginedesigner many options regarding materials, weights, strengths, and heatresistance that can be combined to come up with an optimum design for aspecific engine's goals and requirements.

Having described the present invention, it will be understood by thoseskilled in the art that many changes in construction and widelydiffering embodiments and applications of the invention will suggestthemselves without departing from the scope of the present invention.

1. A method for improving fan case containment in a gas turbine jet engine, the method comprising the steps of: (a) machining a containment ring notch circumferentially into an inner surface towards a front end of the fan case; and (b) seating a containment ring in said containment ring notch through a shrink interference fit.
 2. A method according to claim 1 wherein said machining step further comprises the step of: machining said containment ring notch into said inner surface of the fan case in a first direction, wherein a plurality of grooves are formed and aligned on said inner surface in said first direction.
 3. A method according to claim 2 further comprising the step of: prior to said machining step, forging said containment ring in one piece; and machining said containment ring to a predetermined shape to match with said containment ring notch.
 4. A method according to claim 3 wherein said containment ring is forged from nickel-base super alloy in one piece.
 5. A method according to claim 3 wherein said machining said containment ring step further comprises the step of: machining an outer surface of said containment ring in a second direction, wherein a plurality of grooves are formed and aligned on said outer surface in said second direction; wherein when said inner surface of said containment ring notch and said outer surface of said containment ring are seated together, said plurality of grooves on said inner surface of said containment ring notch and said plurality of grooves on said outer surface of said containment ring align in a cross-hatch manner to each other, increasing the frictional forces between said containment ring notch and said containment ring and reducing the potential for spinning of said containment ring within said containment ring notch.
 6. A method according to claim 3 further comprising the step of: spot welding said containment ring to said containment ring notch in at least one location to prevent said containment ring from spinning in relation to said containment ring notch.
 7. A method according to claim 3 further comprising the step of: bolting said containment ring to at least one flange secured to said containment ring notch to prevent said containment ring from spinning in relation to said containment ring notch.
 8. A method according to claim 3 wherein said machining said containment ring step further comprises the step of: machining said containment ring with a reverse taper, wherein a first outside diameter of said containment ring at a first point towards a front end is less than a second inside diameter of said containment ring at a second point away from said front end.
 9. A method according to claim 1 wherein said machining step further comprising the step of: machining said containment ring notch with a reverse taper, wherein a first inside diameter of the fan case at a first point of said containment ring notch towards said front end is less than a second inside diameter of the fan case at a second point of said containment ring notch located away from said front end.
 10. A method according to claim 1 wherein said seating step further comprises the steps of: heating the fan case to cause an inside diameter of said containment ring notch to increase to a second diameter that is larger than an outside diameter of said containment ring at an ambient temperature; positioning said containment ring in said containment ring notch; and allowing the fan case to cool to said ambient temperature, causing said containment ring notch to want to decrease from said second diameter to said inside diameter, but prevented from doing so by said outside diameter of said containment ring at said ambient temperature, giving rise to said shrink interference fit.
 11. A method according to claim 1 wherein said seating step further comprises the steps of: heating the fan case to cause an inside diameter of said containment ring notch to increase to a second diameter; cooling said containment ring to cause an outside diameter of said containment ring to decrease to a second diameter, wherein said second diameter of said containment ring is smaller than said second diameter of said containment ring notch; positioning said containment ring in said containment ring notch; and allowing the fan case to cool to an ambient temperature causing said containment ring notch to want to decrease from said second diameter to said inside diameter, and allowing said containment ring to warm up to said ambient temperature causing said containment ring to want to increase to said outside diameter, giving rise to said shrink interference fit.
 12. A method according to claim 1 wherein said seating step further comprises the steps of: cooling said containment ring to cause an outside diameter of said containment ring to decrease to a second diameter, wherein said second diameter of said containment ring is smaller than an inside diameter of said containment ring notch; positioning said containment ring in said containment ring notch; and allowing said containment ring to warm up to said ambient temperature causing said containment ring to want to increase to said outside diameter, but prevented from doing so by said inside diameter of said containment ring notch at said ambient temperature, giving rise to said shrink interference fit.
 13. A method according to claim 1 further comprising the steps of: machining at least one stiffening ring notch circumferentially into an outer surface of the fan case; and seating a stiffening ring in said at least one stiffening ring notch, wherein said stiffening ring helps prevent the fan case from going oval under a load and temperature conditions experienced during operation of the gas turbine jet engine.
 14. A method according to claim 13 wherein seating said stiffener ring step further comprises the steps of: heating said stiffening ring to cause a first inside diameter of said stiffening ring to increase to a second inside diameter that is larger than an outside diameter of said at least one stiffening ring notch at an ambient temperature; positioning said stiffening ring in said at least one stiffening ring notch; and allowing said stiffening ring to cool to said ambient temperature, causing said stiffening ring to want to decrease from said second inside diameter to said first inside diameter, but prevented from doing so by said outside diameter of said at least one stiffening ring notch, giving rise to said shrink interference fit.
 15. An apparatus for improving fan case containment in a gas turbine jet engine, the apparatus comprising: a containment ring notch machined circumferentially into an inner surface towards a front end of the fan case; and a containment ring seated in said containment ring notch, wherein said containment ring is seated through a shrink interference fit.
 16. The apparatus according to claim 15 wherein said containment ring is forged from nickel-base super alloy in one piece and machined to a predetermined shape.
 17. The apparatus according to claim 15 wherein an outside diameter of said containment ring is slightly larger than an inside diameter of said containment ring notch at an ambient air temperature, and the fan case is heated to cause said inside diameter of said containment ring notch to increase to a second diameter that is larger than said outside diameter of said containment ring, enabling said containment ring to be positioned in said containment ring notch giving rise to said shrink interference fit when the fan case cools to said ambient temperature.
 18. The apparatus according to claim 17 wherein said containment ring notch is machined with a reverse taper such that a first inside diameter of the fan case at a first point towards said front end is less than a second inside diameter of the fan case at a second point away from said front end, and further wherein said containment ring is machined circumferentially on its outside surface to match said reverse taper.
 19. The apparatus according to claim 15 wherein an outside diameter of said containment ring is slightly larger than an inside diameter of said containment ring notch at an ambient air temperature, and the fan case is heated to cause said inside diameter of said containment ring notch to increase to a second diameter, and said containment ring is cooled to cause an outside diameter of said containment ring to decrease to a second diameter, wherein said second diameter of said containment ring is smaller than said second diameter of said containment ring notch, enabling said containment ring to be positioned in said containment ring notch giving rise to said shrink interference fit when the fan case cools and said containment ring warms up to said ambient temperature.
 20. The apparatus according to claim 15 wherein an outside diameter of said containment ring is slightly larger than an inside diameter of said containment ring notch at an ambient air temperature, and said containment ring is cooled to cause an outside diameter of said containment ring to decrease to a second diameter, wherein said second diameter of said containment ring is smaller than an inside diameter of said containment ring notch, enabling said containment ring to be positioned in said containment ring notch giving rise to said shrink interference fit when said containment ring warms up to said ambient temperature.
 21. The apparatus according to claim 15 further comprising: a plurality of grooves aligned in a first direction on a machined inner surface of said containment ring notch; and a plurality of grooves aligned in a second direction on a machined outer surface of said containment ring; wherein when said inner surface of said containment ring notch and said outer surface of said containment ring are interference shrink fit together, said plurality of grooves on said inner surface of said containment ring notch and said plurality of grooves on said outer surface of said containment ring align in a cross-hatch manner to each other, increasing the frictional forces between said containment ring notch and said containment ring and reducing the potential for spinning of said containment ring within said containment ring notch.
 22. The apparatus according to claim 15 further comprising: a spot weld in at least one location for welding said containment ring to said containment ring notch to prevent said containment ring from spinning in relation to said containment ring notch.
 23. The apparatus according to claim 15 further comprising: at least one flange secured to said containment ring notch, wherein said containment ring is bolted to said at least one flange to prevent said containment ring from spinning in relation to said containment ring notch.
 24. The apparatus according to claim 15 further comprising: at least one stiffening ring notch machined circumferentially into an outer surface of the fan case; and a stiffening ring seated in said at least one stiffening ring notch, wherein said stiffening ring is seated through a shrink interference fit, wherein said stiffening ring helps prevent the fan case from going oval under a load and temperature conditions experienced during operation of the gas turbine jet engine.
 25. The apparatus according to claim 24 wherein said stiffening ring is forged from aluminum in one piece.
 26. The apparatus according to claim 15 wherein an inside diameter of said stiffening ring is slightly smaller than an outside diameter of said at least one stiffening ring notch at ambient air temperature, and said stiffening ring is heated to cause said inside diameter of said stiffening ring to increase to a second diameter that is larger than said outside diameter of said at least one stiffening ring notch, enabling said stiffening ring to be positioned in said at least one stiffening ring notch giving rise to said shrink interference fit when said stiffening ring cools to said ambient temperature.
 27. The apparatus according to claim 15 wherein the fan case is forged from a one of steel, titanium, and aluminum.
 28. The apparatus according to claim 15 wherein the fan case is manufactured from a one of steel, titanium, and aluminum.
 29. The apparatus according to claim 15 wherein the fan case is manufactured from a composite material.
 30. The apparatus according to claim 29 wherein an outside diameter of said containment ring is slightly larger than an inside diameter of said containment ring notch at an ambient air temperature, and said containment ring is cooled to cause said outside diameter of said containment ring to decrease to a second diameter that is smaller than said inside diameter of said containment ring notch, enabling said containment ring to be positioned in said containment ring notch giving rise to an interference fit when said containment ring warms to said ambient temperature.
 31. A method for improving fan case heat resistance in a gas turbine jet engine, the method comprising the steps of: (a) machining a heat resistance ring notch circumferentially into an inner surface towards a middle of the fan case; and (b) seating a heat resistance ring in said heat resistance ring notch through a shrink interference fit.
 32. A method according to claim 31 wherein said machining step further comprises the step of: machining said heat resistance ring notch into said inner surface of the fan case in a first direction, wherein a plurality of grooves are formed and aligned on said inner surface in said first direction.
 33. A method according to claim 32 further comprising the step of: prior to said machining step, making said heat resistance ring from a titanium sheet material that is cut, bent into a cylindrical shape, and welded along a seam; and forming said heat resistance ring to a predetermined shape to match with said heat resistance ring notch.
 34. A method according to claim 32 further comprising the step of: prior to said machining step, forging said heat resistance ring in one piece; and machining said heat resistance ring to a predetermined shape to match with said heat resistance ring notch.
 35. A method according to claim 34 wherein said heat resistance ring is forged from a one of titanium, steel, steel alloy, and aerospace super alloys in one piece.
 36. A method according to claim 34 wherein said machining said heat resistance ring step further comprises the step of: machining an outer surface of said heat resistance ring in a second direction, wherein a plurality of grooves are formed and aligned on said outer surface in said second direction; wherein when said inner surface of said heat resistance ring notch and said outer surface of said heat resistance ring are seated together, said plurality of grooves on said inner surface of said heat resistance ring notch and said plurality of grooves on said outer surface of said heat resistance ring align in a cross-hatch manner to each other, increasing the frictional forces between said heat resistance ring notch and said heat resistance ring and reducing the potential for spinning of said heat resistance ring within said heat resistance ring notch.
 37. A method according to claim 34 further comprising the step of: spot welding said heat resistance ring to said heat resistance ring notch in at least one location to prevent said heat resistance ring from spinning in relation to said heat resistance ring notch.
 38. A method according to claim 34 further comprising the step of: bolting said heat resistance ring to at least one flange secured to said heat resistance ring notch to prevent said heat resistance ring from spinning in relation to said heat resistance ring notch.
 39. A method according to claim 31 wherein said seating step further comprises the steps of: heating the fan case to cause an inside diameter of said heat resistance ring notch to increase to a second diameter that is larger than an outside diameter of said heat resistance ring at an ambient temperature; positioning said heat resistance ring in said heat resistance ring notch; and allowing the fan case to cool to said ambient temperature, causing said heat resistance ring notch to want to decrease from said second diameter to said inside diameter, but prevented from doing so by said outside diameter of said heat resistance ring at said ambient temperature, giving rise to said shrink interference fit.
 40. A method according to claim 31 wherein said seating step further comprises the steps of: heating the fan case to cause an inside diameter of said heat resistance ring notch to increase to a second diameter; cooling said heat resistance ring to cause an outside diameter of said heat resistance ring to decrease to a second diameter, wherein said second diameter of said heat resistance ring is smaller than said second diameter of said heat resistance ring notch; positioning said heat resistance ring in said heat resistance ring notch; and allowing the fan case to cool to an ambient temperature, causing said heat resistance ring notch to want to decrease from said second diameter to said inside diameter, and allowing said heat resistance ring to warm up to said ambient temperature causing said heat resistance ring to want to increase to said outside diameter, giving rise to said shrink interference fit.
 41. A method according to claim 31 wherein said seating step further comprises the steps of: cooling said heat resistance ring to cause an outside diameter of said heat resistance ring to decrease to a second diameter, wherein said second diameter of said heat resistance ring is smaller than an inside diameter of said heat resistance ring notch; positioning said heat resistance ring in said heat resistance ring notch; and allowing said heat resistance ring to warm up to said ambient temperature causing said heat resistance ring to want to increase to said outside diameter, but prevented from doing so by said inside diameter of said heat resistance ring notch at said ambient temperature, giving rise to said shrink interference fit.
 42. An apparatus for improving fan case heat resistance in a gas turbine jet engine, the apparatus comprising: a heat resistance ring notch machined circumferentially into an inner surface towards a middle of the fan case; and a heat resistance ring seated in said heat resistance ring notch, wherein said heat resistance ring is seated through a shrink interference fit.
 43. The apparatus according to claim 42 wherein said heat resistance ring is forged from a one of titanium, steel, steel alloy, and aerospace super alloys in one piece and machined to a predetermined shape.
 44. The apparatus according to claim 42 wherein said heat resistance ring is made from a one of a titanium, steel, steel alloy, and aerospace super alloys sheet material that is cut, bent into a cylindrical shape, and welded along a seam and formed to a predetermined shape to match with said heat resistance ring notch.
 45. The apparatus according to claim 42 wherein an outside diameter of said heat resistance ring is slightly larger than an inside diameter of said heat resistance ring notch at an ambient air temperature, and the fan case is heated to cause said inside diameter of said heat resistance ring notch to increase to a second diameter that is larger than said outside diameter of said heat resistance ring, enabling said heat resistance ring to be positioned in said heat resistance ring notch giving rise to said shrink interference fit when the fan case cools to said ambient temperature.
 46. The apparatus according to claim 42 wherein an outside diameter of said heat resistance ring is slightly larger than an inside diameter of said heat resistance ring notch at an ambient air temperature, and the fan case is heated to cause said inside diameter of said heat resistance ring notch to increase to a second diameter, and said heat resistance ring is cooled to cause an outside diameter of said heat resistance ring to decrease to a second diameter, wherein said second diameter of said heat resistance ring is smaller than said second diameter of said heat resistance ring notch, enabling said heat resistance ring to be positioned in said heat resistance ring notch giving rise to said shrink interference fit when the fan case cools and said heat resistance ring warms up to said ambient temperature.
 47. The apparatus according to claim 42 wherein an outside diameter of said heat resistance ring is slightly larger than an inside diameter of said heat resistance ring notch at an ambient air temperature, and said heat resistance ring is cooled to cause an outside diameter of said heat resistance ring to decrease to a second diameter that is smaller than said inside diameter of said heat resistance ring notch, enabling said heat resistance ring to be positioned in said heat resistance ring notch giving rise to said shrink interference fit when said heat resistance ring warms up to said ambient temperature.
 48. The apparatus according to claim 42 further comprising: a plurality of grooves aligned in a first direction on a machined inner surface of said heat resistance ring notch; and a plurality of grooves aligned in a second direction on a machined outer surface of said heat resistance ring; wherein when said inner surface of said heat resistance ring notch and said outer surface of said heat resistance ring are interference shrink fit together, said plurality of grooves on said inner surface of said heat resistance ring notch and said plurality of grooves on said outer surface of said heat resistance ring align in a cross-hatch manner to each other, increasing the frictional forces between said heat resistance ring notch and said heat resistance ring and reducing the potential for spinning of said heat resistance ring within said heat resistance ring notch.
 49. The apparatus according to claim 42 further comprising: a spot weld in at least one location for welding said heat resistance ring to said heat resistance ring notch to prevent said heat resistance ring from spinning in relation to said heat resistance ring notch.
 50. The apparatus according to claim 42 further comprising: at least one flange secured to said heat resistance ring notch, wherein said heat resistance ring is bolted to said at least one flange to prevent said heat resistance ring from spinning in relation to said heat resistance ring notch.
 51. The apparatus according to claim 42 wherein the fan case is forged from aluminum.
 52. The apparatus according to claim 42 wherein the fan case is manufactured from aluminum.
 53. The apparatus according to claim 42 wherein the fan case is manufactured from a composite material. 